If $x \boxdot y = 4x-8$ and $x \bigtriangledown y = 4x^{2}+y^{2}$, find $6 \boxdot (5 \bigtriangledown 6)$.
Explanation: We don't need to find $5 \bigtriangledown 6$ because $x \boxdot y$ depends only on the left operand. Find $6 \boxdot y$ $ 6 \boxdot y = (4)(6)-8$ $ \hphantom{6 \boxdot y} = 16$.